Anodizing resistant components and methods of use thereof

ABSTRACT

Methods and structures for forming anodization layers that protect and cosmetically enhance metal surfaces are described. In some embodiments, methods involve forming an anodization layer on an underlying metal that permits an underlying metal surface to be viewable. In some embodiments, methods involve forming a first anodization layer and an adjacent second anodization layer on an angled surface, the interface between the two anodization layers being regular and uniform. Described are photomasking techniques and tools for providing sharply defined corners on anodized and texturized patterns on metal surfaces. Also described are techniques and tools for providing anodizing resistant components in the manufacture of electronic devices.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 61/689,170, filed May 29, 2012, andentitled “COMPONENT FOR AN ELECTRONIC DEVICE,” which is incorporatedherein by reference in its entirety and for all purposes.

FIELD OF THE DESCRIBED EMBODIMENTS

The described embodiments relate generally to anodizing processes. Morespecifically, embodiments describe methods for producing anodizationlayers that can protect and enhance the appearance of metal surfaces.Tools and methods for accommodating anodizing processes performed onenclosures for electronic devices are described.

BACKGROUND

Consumer products such as personal computers and electronic devicesoften have metal surfaces. During the manufacture of the consumerproducts, these metal surfaces typically undergo a number of operationsin order to make the metal parts functional as well as cosmeticallyappealing. For instance, the metal housing of a consumer product canundergo machining operations to form features in the metal and designoperations to form patterns and logos on the metal surfaces.

In addition, metal surfaces are usually treated so as to be more wearand corrosion resistant. For example, aluminum surfaces are typicallyanodized to convert part of the aluminum to aluminum oxide. Aluminumoxide films are harder than aluminum, thereby providing a protectivelayer over the softer aluminum. Consumer products such as electronicdevices tend to have sharp corners and edges that make it difficult toform a consistent and cosmetically appealing anodization film thereon.

SUMMARY

This paper describes various embodiments that relate to techniques andtools for providing anodizing resistant components. Methods can be usedduring the manufacture of electronic devices.

According to one embodiment, a method of forming a metal enclosure foran electronic device is described. The method involves coupling a firstsection and a second section of the enclosure by injection molding afirst shot component of a coupling member into and around lockingmembers positioned in the first section and second section of theenclosure. The first shot component is made of a high strengthstructural material that is resistant to a subsequent anodizing process.The method also involves forming a second shot component, which at leastpartially covers the first shot component. The second shot is made of adifferent material than the first shot component. The second shotcomponent is resistant to the subsequent anodizing process. The methodalso involves anodizing the enclosure. The metal portions of theenclosure are anodized and the first and second shot components maintainstructural integrity and appear substantially unmarred by the anodizingprocess.

According to another embodiment, another method of forming a metalenclosure for an electronic device is described. The method involvesforming a first shot component configured to physically couple twosections of the enclosure. The first shot is made of a high strengthstructural material. The method also involves forming a second shotcomponent that completely surrounds the surface of the first shotcomponent. The second shot is made of a different material than thefirst shot component. The second shot component is resistant to asubsequent anodizing process. The method additionally involves anodizingthe enclosure. The metal portions of the enclosure are anodized and thefirst and second shot components maintain structural integrity andappear substantially unmarred by the anodizing process.

According to an additional embodiment, a method for forming a plasticcoupling member in an enclosure is described. The method involvesforming a first shot component by injection molding the first shotcomponent into interfaces of the enclosure. The first shot component isconfigured to physically couple two sections of the enclosure. The firstshot component is made of a high strength structural material that isunaffected by a subsequent anodizing process. The method also involvesforming a second shot component, wherein a portion of the second shotcomponent forms an exterior surface of the enclosure. The second shotcomponent is made of a different material than the first shot componentand formed by injection molding the second shot component onto at leasta portion of the surface of the first shot component. The second shotcomponent is configured to cosmetically enhance the first shot componentand the exterior surface of the enclosure. The second shot component isresistant to the subsequent anodizing process and blasting process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a general double anodizing process inaccordance with described embodiments.

FIG. 2 is a schematic isometric view of a portable electronic deviceconfigured in accordance with an embodiment of the disclosure.

FIG. 3 is a schematic isometric view of at least a portion of asubassembly of the electronic device of FIG. 2.

FIG. 4 is a flowchart illustrating details of a double anodizing processgraphically presented in FIGS. 5A-5E.

FIGS. 5A-5E graphically illustrate selected views of a part undergoing adouble anodizing process in accordance with described embodiments.

FIGS. 6A and 6B graphically illustrate the microstructures of selectedprofiles of two different anodization layers produced by two differentanodizing processes.

FIGS. 7A and 7B graphically illustrate selected profiles of two separateparts that have undergone two different anodizing processes.

FIG. 8 is a graph showing the current density or voltage change as afunction of time for a slow ramp up anodizing procedure in accordancewith described embodiments.

FIGS. 9A-9C are schematic top down views of a portion of a metal surfaceundergoing a slow ramp up anodizing procedure in accordance withdescribed embodiments.

FIG. 9D is a flow chart illustrating details of a process for forming abarrier layer and transparent anodizing layer on a substrate inaccordance with described embodiments.

FIG. 10A graphically illustrates a selected profile of a part having anangled surface undergoing a single anodizing process.

FIGS. 10B-10E graphically illustrate selected profiles of a part havingan angled surface undergoing a double anodizing process in accordancewith described embodiments.

FIG. 11 is a flowchart illustrating details of an anodizing processgraphically presented in FIGS. 12A-12F.

FIGS. 12A-12F graphically illustrate selected profiles of a partundergoing an anodization process which includes a highlightingtechnique in accordance with the described embodiments.

FIGS. 13A and 13B graphically illustrate close up views of selectedportions of a photomask for developing negative type and positive typephotoresist, respectively, in accordance with described embodiments.

FIGS. 14A-14D graphically illustrate selected portions of a photomask,photoresist and substrate using a photomask in accordance with describedembodiments.

FIG. 14E is a flow chart illustrating details of process for forming apattern on a substrate using a photomask with pre-distortion features inaccordance with described embodiments.

FIGS. 15A-15B illustrate views of an enclosure for an electronic devicehaving anodizing resistant plastic coupling members in accordance withdescribed embodiments.

FIG. 16 illustrates a close up view of a portion of FIG. 15B inaccordance with described embodiments.

FIG. 17 is a flow chart illustrating details of a process for forming ananodizing resistant plastic member for an enclosure in accordance withdescribed embodiments.

DETAILED DESCRIPTION OF SELECTED EMBODIMENTS

The following disclosure describes various embodiments of electronicdevices, such as portable electronic devices including, for example,mobile telephones. Certain details are set forth in the followingdescription and Figures to provide a thorough understanding of variousembodiments of the present technology. Moreover, various features,structures, and/or characteristics of the present technology can becombined in other suitable structures and environments. In otherinstances, well-known structures, materials, operations, and/or systemsare not shown or described in detail in the following disclosure toavoid unnecessarily obscuring the description of the various embodimentsof the technology. Those of ordinary skill in the art will recognize,however, that the present technology can be practiced without one ormore of the details set forth herein, or with other structures, methodsand components.

Representative applications of methods and apparatuses according to thepresent application are described in this section. These examples arebeing provided solely to add context and aid in the understanding of thedescribed embodiments. It will thus be apparent to one skilled in theart that the described embodiments may be practiced without some or allof these specific details. In other instances, well known process stepshave not been described in detail in order to avoid unnecessarilyobscuring the described embodiments. Other applications are possible,such that the following examples should not be taken as limiting.

In the following detailed description, references are made to theaccompanying drawings, which form a part of the description and in whichare shown, by way of illustration, specific embodiments in accordancewith the described embodiments. Although these embodiments are describedin sufficient detail to enable one skilled in the art to practice thedescribed embodiments, it is understood that these examples are notlimiting, such that other embodiments may be used, and changes may bemade without departing from the spirit and scope of the describedembodiments.

In the detailed description, reference is made to metal or metal parts.In certain preferred embodiments, the metal is aluminum or aluminumalloy. However, a person of skill in the art would recognize that in thecontext of the present invention, the term metal refers to any suitablemetal containing material capable of undergoing an anodization process,including pure elemental metal as well as a metal alloy or metalmixture.

The embodiments described herein relate to methods and structures forproviding protective anodization layers on a metal part. Methods includea double anodizing process whereby the part undergoes a first anodizingprocess to create a first (or primary) anodization layer on a portion ofthe metal surface and a second anodizing process to create a second (orsecondary) anodization layer which is adjacent to and in contact withthe first anodization layer on a different portion of the metal surface.Described embodiments include methods for forming first and secondanodization layers on angled metal surfaces wherein the anodizationlayers interface at edges of the metal part, the interface of theanodization layers being uniform and cosmetically appealing. In someembodiments, the first anodization layer can overlay a first metalsurface having a first finish and the second anodization layer canoverlay a second metal surface having a second finish. For example, thefirst finish can be rough or matted and the second finish can be highlyreflective and/or have a design such as a logo or company mark.

In some embodiments, the second anodization layer is substantiallytransparent in order to reveal features of the underlying metal surface.The underlying metal surface can have a reflective shine or ornamentalfeatures which would be viewable through the transparent secondanodization layer. In cases wherein the second anodization layer istransparent, the anodization film is thick enough to withstand wear. Thethickness of the second anodization layer closely approximates thethickness of the first anodization layer so as to provide a smoothsurface with substantially no offset of either the first or secondanodization layer. This offset could also be controlled to improvedurability (e.g., one layer could be made sub-flush to another, whichcan potentially make it less likely to be scratched).

FIG. 1 is a flowchart showing a general double anodizing process inaccordance with described embodiments. At 102, a first anodization layeron a portion of an underlying surface is formed using a first anodizingprocess. The underlying surface can be a metal surface having a firstfinish, the first finish having any suitable characteristic and quality.For example, the first finish can be polished and smooth, machined orground, or textured and rough. In one embodiment, the first anodizationlayer can be formed using a first anodizing process. The first anodizingprocess generally uses standard process parameters such as typicalanodizing electric current density, bath temperature and anodizingduration. For example, the first anodizing process can be characterizedby a bath temperature ranging from about 15 to 25 degrees C., anelectric current density of about 1.5 Amp/dm² to about 2.0 Amp/dm², andan anodizing duration of about 10 to 40 minutes. The anodized layerusing these parameters can be characterized as being substantiallyopaque, thus preventing an unobscured viewing of underlying features.Once the first anodization layer has been formed, an adjoining secondanodization layer can be formed at a contiguous portion of the metalsurface 104. The second anodizing process generally uses a lowerelectric current, higher bath temperature and longer anodizing durationthan the first anodizing process. For example, the second anodizingprocess can be characterized as having an electric current density ofabout 0.4 Amp/dm² to about 1.0 Amp/dm², bath temperature of about 20 to30 degrees C., and duration of greater than about 15 minutes. Theseanodization parameters result in a second anodization layer that has adifferent anodic oxide pore structure than that of the first anodizationlayer, creating a second anodization layer that can be characterized assubstantially transparent. Since the second anodization layer can besubstantially transparent, it allows a much less obscured viewing ofunderlying surface features that would not otherwise be possible usingthe first anodizing process. It should be noted that in some cases therelative transparency of the first anodization layer can be increased byreducing the overall thickness of the first anodization layer. However,this thinning of the first anodization layer generally reduces theprotective properties of the first anodization layer. In contrast, theinherently higher degree of transparency afforded by the secondanodization layer provides excellent viewability while maintaining thesuperior protective properties of the un-thinned second anodizationlayer.

Due to the different properties afforded the first and secondanodization layers, an interface between the first and secondanodization layers can be naturally well defined. Since the interface ofthe first anodization layer and the second anodization layer is regular,a uniform and cosmetically appealing line between the first and secondanodization layers can be provided. Details about the regular, a uniformand cosmetically appealing interface between the first and secondanodization layers will be described below.

As discussed previously, methods of the embodiment can be applied in thefabrication of personal computers and electronic devices, includingportable electronic devices. FIG. 2 is a schematic isometric view of aportable electronic device 10 (“electronic device 10”), such as acellular telephone, configured in accordance with embodiments of thedisclosure. In the illustrated embodiment, the electronic device 10includes a body 11 carrying a display 12 that allows a user to interactwith or control the electronic device 10. For example, the display 12includes a cover or cover glass 14 that is operably coupled to a frame,housing, or enclosure 16. In certain embodiments, the display 12 and/orcover 14 can include touch sensitive features to receive input commandsfrom a user. Moreover, in certain embodiments a cover can be positionedon one side of the electronic device 10, or a cover can be positioned onopposing sides of the electronic device 10. As described in detailbelow, the enclosure 16 and the cover 14 at least partially house orenclose several internal features of the electronic device 10.

In the embodiment illustrated in FIG. 2, the enclosure 16 also at leastpartially defines several additional features of the electronic device10. More specifically, the enclosure 16 can include audio speakeroutlets 18, a connector opening 20, an audio jack opening 22, a cardopening 24 (e.g., SIM card opening), a front facing camera 26, a rearfacing camera (not shown in FIG. 1), a power button (not shown in FIG.1), and one or more volume buttons (not shown in FIG. 1). Although FIG.1 schematically illustrates several of these features, one of ordinaryskill in the art will appreciate that the relative size and location ofthese features can vary.

In certain embodiments, the enclosure 16 can be made from a metallicmaterial. For example, the enclosure 16 can be made from aluminum, suchas 6063 Aluminum. In other embodiments, however, the enclosure 16 can bemade from other suitable metals and/or alloys. According to additionalfeatures of the embodiment shown in FIG. 2, the enclosure 16 includesopposing edge portions 30 (identified individually as a first edgeportion 30 a and a second edge portion 30 b) extending around aperiphery of the body 11. In certain embodiments, one or both of theedge portions 30 can have a chamfered or beveled profile. As describedin detail below, the chamfered edge portions 30 can be processedrelative to the enclosure 16 to provide an aesthetically appealingappearance. For example, the exterior surface of the enclosure 16 can betreated and the edge portions 30 can subsequently be treated. In oneembodiment, for example, a first anodization process can be applied tothe enclosure 16 and a second subsequent anodization process can beapplied to the edge portions 30. Additional suitable surface treatments,including intermediary surface treatments, can be applied to theenclosure 16 and/or the edge portions 30. In still further embodiments,the edge portions 30 can have other suitable profiles or shapesincluding and/or surface treatments.

FIG. 3 is a schematic isometric view of at least a portion of asubassembly 40 of the electronic device of FIG. 2. In the embodimentillustrated in FIG. 3, the subassembly 40 includes the enclosure 16coupled to a cover, such as the cover 14 shown in FIG. 2. As shown inFIG. 3, the enclosure 16 includes a first enclosure portion 42 coupledto a second enclosure portion 44, which is in turn coupled to a thirdenclosure portion 46. More specifically, the enclosure 16 includes afirst connector portion 48 that couples the first enclosure portion 42to the second enclosure portion 44. The enclosure also includes a secondconnector portion 50 that couples the second enclosure portion 44 to thethird enclosure portion 46. In certain embodiments, the first, second,and third enclosure portions 42, 44, and 46 can be metallic and thefirst and second connector portions 48 and 50 can be made from one ormore plastic materials. For example, each of the first and secondconnector portions 48 and 50 can be formed from a two-shot plasticprocess that includes a first structural plastic portion that enjoinsthe corresponding enclosure portions and a second cosmetic plasticportion that at least partially covers the first plastic portions. Theseplastic portions can be configured to withstand harsh manufacturingprocesses and chemicals that may be used to form and process theenclosure, including chemicals used in the anodization process, UV lightexposure, abrasives from a blasting process, coolants used in CNC stepsand chemicals used to strip masking materials. These chemicals caninclude strong acids or bases applied at high or low temperatures andheld for extended periods of time. Details regarding suitable two-shotplastic techniques are described below. In further embodiments, theenclosure portions 42, 44, and 46 and/or the connecting portions 48 and50 can be made from other suitable materials including metallic,plastic, and other suitable materials.

According to additional features of the embodiment illustrated in FIG.3, the enclosure 16 can include one or more low resistance conductiveportions 52 (shown schematically) for grounding purposes. Conductiveportions 52 can include, for example, of aluminum which can shield RFwaves. The conductive portion 52 can be formed by removing one or morelayers or portions of the enclosure 16 to provide a lower resistancethrough the enclosure 16 for antenna transmissions or communications. Incertain embodiments, for example, the conductive portion 52 can beformed by laser etching or otherwise removing or etching an anodizedportion of the enclosure 16. The exposed surfaces of conductive portion52 can then be chemically treated to retain its electrical conductivity.Examples of suitable chemical treatment include chromate andnon-chromate conversion coatings to passivate conductive portion 52.These coatings can be applied using techniques including spraying andbrushing using a paint brush. The conductivity of the exposed portion52, as well as through different portions of the enclosure 16, can betested using suitable techniques such as using resistance using probesat different points of exposed portion 52 and enclosure 16 to assurethat ground can be established though housing 16.

The illustrated subassembly 40 also includes several inserts 54 thatprovide increased structural connection strength relative to theenclosure 16. In embodiments where the enclosure 16 is formed fromaluminum, for example, inserts 54 can provide increased strength anddurability. In some embodiments, inserts 54 are conductive so that theycan serve as electrical grounding features. In certain embodiments theinserts 54 can include threaded inserts or nuts that are configured tothreadably engage a corresponding fastener. In some instances, inserts54 are added to enclosure 16 before the part undergoes subsequentanodizing processes. In these cases, it is advantageous for inserts 54to be made of material, such as titanium, that can withstand thechemically harsh anodizing process. If, for example, the inserts weremade of steel or brass, they could become corroded by the anodizingchemicals which could destroy the part and also contaminate theanodizing bath. Titanium can anodize, but under the conditions used foranodizing aluminum, will anodize minimally and create little filmgrowth. Thus, the titanium inserts will remain conductive and thereforesuitable for electrical grounding, even after undergoing an aluminumanodizing process. In addition, since anodization will occur minimallyon titanium, the geometry of any threaded regions of the inserts willremain substantially the same. It should be noted that in addition totitanium, other suitable hard metals materials can be used for theinserts, including hard aluminum alloys such as 7075 aluminum alloy.Inserts made of softer aluminum alloys can be used; however the softeraluminum inserts would anodize in the aluminum anodizing bath.Therefore, in order to keep the aluminum inserts electrically conductiveand to retain any threaded geometry, it can be necessary to mask thealuminum inserts using, for example polymer plugs, prior to exposure tothe anodizing bath. This masking process adds a manufacturing procedureand manual labor to the process.

According to yet additional features of the subassembly 40 shown in FIG.3, the cover 14 can be securely coupled and/or offset (if desired)relative to the enclosure 16. More specifically, the cover 14 can bealigned with a reference plane or datum relative to the enclosure 16,and the enclosure 16 (and more specifically the first enclosure portion42, the second enclosure portion 44, and/or the third enclosure portion46) can include one or more access opening 56 to urge or bias the cover14 relative to the enclosure 16 for secure attachment (e.g., adhesiveattachment) while maintaining relatively tight tolerances between thecoupled portions.

According to additional embodiments of the disclosure, the cover 14 canbe made from a glass, ceramic, and/or glass-ceramic material. In oneembodiment, for example, the cover 14 can be made from a glass withspecific portions or volumes of the glass formed with ceramicproperties. In other embodiments, however, the cover 14 can be formedfrom alumina silica based pigmented glass.

As mentioned previously, embodiments described herein provide methodsfor forming a protective anodization layer or layers on exposed metalsurfaces of an electronic device, such as the portable electronic deviceshown in FIGS. 2 and 3. FIGS. 4 and 5A-5E illustrate steps involved inan anodizing process in accordance with embodiments of the disclosure.FIG. 4 is a flowchart showing process steps. FIGS. 5A-5E graphicallypresent views of a portion of a part undergoing the process described inFIG. 4. In the following narrative, reference will be made to theflowchart of FIG. 4 in conjunction with the graphical presentations ofFIGS. 5A-5E.

Process 400 begins at 402 (corresponding to FIG. 5A) where a maskingoperation is performed on metal part 500 having a first surface 502 anda second surface 504. In FIGS. 5A-5E, first 502 and second 504 surfacesare contiguous portions of a surface of metal part 500. Mask 506 isformed on and is configured to protect second surface 504 fromsubsequent processes. Metal part 500 can be made of any suitable metalsuch as aluminum, stainless steel or titanium. In addition, metal part500 can include other materials such as ceramic and ceramic containingmaterials. In particular embodiments, metal part 500 can be made of anyof various grades of aluminum alloy including those in the 6000 series(e.g., 6063 and 6061), 5000 series (e.g., 5054 and 5052) and 7000series. The use of different types and grades of metal will require thatsubsequent processes, such as anodizing, texturing and polishingprocesses, to have different parameters depending on the materialproperties and hardness of the metal.

Prior to masking, the part can optionally undergo cleaning operations toremove unwanted surface defects, dirt, dust, and so forth that can causedefects or otherwise adversely affect subsequent anodization processes.For example, the surface cleaning operations can include well knownprocesses such as a wet polish. The wet polish can use slurry such asaluminum oxide slurry that in conjunction with a mechanical polisher canbe used to remove machine marks and to create an even surface forblasting or other texturing process. In addition, the wet polish can beused to increase the gloss of any subsequent texturing procedure. Insome cases, a mechanical chemical lapping can be performed using acidicor alkali slurry (e.g., aluminum oxide or silicon oxide) that canprovide a mirror finish on the metal surface. After the optionalpolishing, artwork (e.g., company logo and/or text) can optionally beformed on a mirror finished metal surface, using for example, aphotolithography process.

In certain embodiments, the masking and artwork procedures are performedtogether. The mask is a photoresist that can be applied on the part,using for example a spray coating operation. In certain embodiments,selected portions corresponding to the pattern of the artwork are thenUV cured and the uncured portions removed leaving behind covered mirrorfinished surfaces corresponding to the artwork pattern. In some cases,UV curing can include the use of a UV laser. Other suitable maskingtechniques can include screen printing and pad printing processes. Insome embodiments, the photoresist used to cover the artwork is formedfrom a photomask that has pre-distortion features at certain regions ofthe photomask in order to provide sharply defined corners in theresulting artwork on the part. Details of embodiments usingpre-distorted photomasks will be described below with reference to FIGS.13A, 13B and 14A-14D.

After second surface 504 of metal part is masked, the part can undergoan optional procedure to add texture to first surface 502. For example,a blasting operation can be performed whereby the part is exposed to ablasting media. In one embodiment, the blasting media takes the form ofzirconia applied under about 1 bar of pressure. Alternatively, achemical etching process can be used to impart a textured surface with adifferent quality than a blasted surface. Since second surface 504 isprotected by mask 506, it will not be subject to the texturing orblasting and will retain previously provided surface features such asartwork and/or mirror polish.

At 404 (corresponding to FIG. 5B), the part undergoes a first anodizingprocess wherein first surface 502 is anodized forming a primaryanodization layer 508 adjacent to and in contact second surface 504,wherein the second surface 504 is not affected due to protection by mask506. Since anodizing involves converting a portion of a metal surface toan oxide layer, dashed line 514 represents the location where firstsurface 502 existed prior to the first anodizing process. Edge 512 ofprimary anodization layer 508 is adjacent to second portion 504 of themetal surface and is defined by an edge of mask 506. Prior toanodization, the part can optionally undergo cleaning operations toremove unwanted surface particles caused by previous processes that cancause defects or otherwise adversely affect subsequent anodizationprocesses. Surface operations can include well known processes such as adegreasing operation using, for example a Na₃PO₄ solution, to removesurface impurities such as grease from machining or oils from handling;a chemically polishing using for example a H₃PO₄ solution bath to changethe surface texture for cosmetic reasons; and a desmut operation using,for example a HNO₃, to remove residues from previous processes such asintermetallic particles at the surface of alloyed aluminum and to etchaway any aluminum oxide passivation layer in preparation for anodizing.The first anodizing process at 404 typically involves use of an H₂SO₄bath solution at a temperature of about 15 to 25 degrees C. In someembodiments, the quality of the anodization layer can be controlled byusing a constant current density. In some embodiments, the currentdensity is set to about 1.5 to 2.0 A/dm². It is also possible to controlthe quality of the anodization by setting a constant voltage. It shouldbe noted that target voltage can vary depending on the size of the part.In general, the duration of anodization will determine the thickness ofthe primary anodization layer 508, which is preferably less than about50 microns thick, more preferably less than about 25 microns thick. Incosmetic applications, primary anodization layer 508 is preferably lessthan about 15 microns thick. In certain embodiments, the anodization isperformed for approximately 10 to 40 minutes resulting in a primaryanodization layer 508 having a thickness of about 8 to 12 microns. Afteranodization is complete the part optionally undergoes a sealingoperation using, for example a nickel acetate solution.

At 406 (corresponding to FIG. 5C), a portion of metal surface isexposed, including at least a portion of second surface 504. In the partshown in FIG. 5C, second surface 504 is exposed by removing mask 506.After mask 506 is removed, primary anodization layer 508 retains edge512 adjacent to second surface 504. Second surface 504 retains anypreviously provided artwork, texturing or polishing. In addition, insome embodiments, a section of primary anodization layer 508 can beremoved to expose a portion of the underlying metal. Metal exposure canbe accomplished by using, for example, a cutting procedure or a laser orchemical etch procedure. Details regarding a cut part in accordance withsome embodiments are described below with reference to FIGS. 10B-10E.

At 408 (corresponding to FIG. 5D), the part undergoes a second anodizingprocess, whereby a secondary anodization layer 510 is formed. Secondaryanodization layer 510 is adjacent to and in contact with primaryanodization layer 508. The second anodizing process occurs substantiallyonly on exposed metal surfaces, such as second surface 504. Metalsurfaces that have already been anodized by the first anodizing process404 are protected from the second anodizing process 408 by primaryanodization layer 508 which acts as a natural mask. This is becauseprimary anodization layer 508 includes AlO₂ which is non-conductive andtherefore not able to conduct the current required as a driving force inan electrochemical anodizing process. The resultant part 500 at FIG. 5Dhas two anodization layers 508 and 510 contacting at an interfacedefined by edge 512. In some embodiments, second anodizing process 408uses different process parameters than first anodizing process 404,resulting in secondary anodization layer 510 having different filmcharacteristics than primary anodization layer 508. In certainembodiments, second anodization process 408 uses process parameters thatcan provide a substantially transparent anodization layer. Processparameters for creating a transparent anodization layer are described indetail below with reference to FIGS. 6A and 6B.

In some embodiments, after second anodizing process 408 is complete, thepart can optionally undergo a laser etch to remove selected portions ofprimary anodization layer 508. For example, selected portions of theprimary anodization layer can be removed to expose conductive aluminumareas suitable for electrical grounding. The laser etched areas wherethe anodization layer has been removed can be treated with a conversioncoating to ensure that the area retains conductivity using, for example,a chromate or non-chromate conversion coating treatment.

FIG. 5E illustrates another view of part 500 after undergoing the doubleanodizing process of 400. FIG. 5E shows a top down view of a largerportion of part 500, wherein FIG. 5D corresponds to section view 516. Asshown in FIG. 5E, secondary anodization layer 510 is disposed adjacentto primary anodization layer 508. As shown by FIGS. 5D and 5E, theinterface between first 508 and second 510 anodization layers is definedby edge 512 of primary anodization layer 508. The resultant part 500 atFIG. 5D has two anodization layers 508 and 510 which can have differentfilm qualities and can appear different from each other from anobserver's perspective, such as a user of an electronic device. Forexample, if primary anodization layer 508 is opaque and secondaryanodization layer 510 is transparent, a user can only view the portionof metal surface below secondary anodization layer 510.

As described above with reference to FIGS. 5A-5E, secondary anodizationlayer 510 can be substantially transparent. The process parameters forforming a transparent anodization films are generally different fromprocess parameters for forming substantially opaque anodization films.For example, a transparent anodizing process typically uses anelectrical current density of about 0.4 to 1.0 A/dm², which issubstantially lower than other anodizing processes such as the firstanodizing process 404 described above and conventional anodizingprocesses. Instead of a constant current density, a constant voltage canbe used to form a transparent anodization layer. For example, a lowervoltage than conventional anodizing processes can be used. It isbelieved that the lower current density or voltage results in a smalleraverage pore size and finer pore structure in the resultant anodizationlayer. Pores are vertical voids that naturally form in themicrostructure of an anodization film during an anodization process. Inaddition, a bath temperature of about 20 to 30 degrees C. is typicallyused to form the transparent anodization layer, which is substantiallyhigher than, for example, the bath temperature of the first anodizingprocess 404 described above. It is believed that the higher bathtemperature results in an increased pore density. The combination of thefiner pore structure and increased pore density manifests in a moretransparent anodization layer as well providing a glossier surface onthe anodization layer compared to conventional anodization layers.Details regarding physical characteristics and microstructure of atransparent anodization layer in accordance with described embodimentswill be described below with reference to FIGS. 6A and 6B.

The anodizing duration for forming a transparent anodization layer canvary depending on other process parameters and on the desired thicknessof the resultant anodization layer. In addition, a film growth maximumcan reached given certain process parameters such as current density,voltage and bath temperature. For applications such as the partdescribed above with reference to FIGS. 4 and 5A-5E, anodizing istypically performed for more than about 15 minutes, resulting in atransparent anodization layer having a thickness of about 7 to 9microns.

As described above, the microstructure of a transparent anodizationlayer in accordance with described embodiments has a different pore sizeand density characteristics compared to opaque anodization layers. Toillustrate, FIGS. 6A and 6B graphically illustrate differences in thefilm characteristics of a transparent anodization layer and asubstantially opaque anodization layer, such as first anodization layer508 of FIGS. 5A-5E. FIGS. 6A and 6B depict close-up views of selectedprofiles of anodization layers formed using two different anodizingprocesses on an aluminum (Al-6063) substrate. As mentioned above, anodicfilms can have porous microstructures with pores formed within the metaloxide material. FIG. 6A depicts the porous microstructure of ananodization layer 600 formed on barrier layer 614, which is in turnformed on aluminum substrate 612. Barrier layer 614 is a thin denselayer of uniform thickness that is the initial layer of oxide growth onmetal substrate 612 during the anodization process. Details regardingthe formation of a barrier layer in accordance with describedembodiments are described below with reference to FIGS. 8 and 9A-9C.Aluminum substrate can have any suitable surface features such as atextured surface from, for example a blasting procedure or etchingprocedure. Anodization layer 600 is formed using a current density ofbetween about 1.5 to 2.0 A/dm² and electrolyte (bath) temperature ofbetween about 15 to 25 degrees C. for between about 10-40 minutes (firstanodizing process 404). The resulting anodization layer (or metal oxidelayer) 600 has pores 602 that have an average pore diameter of about11-13 nm formed within metal oxide having cell walls 604 with an averagewall thickness of about 5-6 nm. FIG. 6B depicts the porousmicrostructure of an anodization layer (or metal oxide layer) 606 formedon barrier layer 618 and aluminum substrate 616. Aluminum substrate 616can have any suitable surface features such as a highly reflectiveshine. Anodization layer 606 is formed using a current density ofbetween about 0.4 to 1.0 Amps/dm² and electrolyte temperature of betweenabout 20 to 30 degrees C. for a duration of more than about 15 minutes(second anodizing process 408). The resulting anodization layer 606 haspores 608 that have an average pore diameter of about 6-9 nm formedwithin metal oxide having cell walls 610 with an average wall thicknessof about 4-5 nm. Thus, anodization layer 606 has approximately 2 to 3times higher pore density than anodization layer 600. In addition, theaverage pore diameter of anodization layer 606 is smaller than theaverage pore diameter of anodization layer 600. The densely packed poresof anodization layer (or metal oxide layer) 606 provide a lighttransmissible path between a top surface of anodization layer (or metaloxide layer) 606 and barrier layer 618, making anodization layer 606substantially transparent. Barrier layer 618 is very thin and generallydoes not impede the transmission of light. Thus, when incident lightdirected at anodization layers 600 and 606, anodization layer 606 ismore likely to permit light, such as from the external environment, topass to the surface of underlying aluminum substrate 616, reflect off ofaluminum substrate 616, and be transmitted back through anodizationlayer 606 and to the external environment. In this way, anodizationlayer 606 can allow a substantially unobstructed view by an observer ofunderlying aluminum substrate 616. Underlying aluminum substrate 616 caninclude surface features, such as a shiny reflective surface, surfacetexture such as a blasted surface, or artwork that can be viewable froman observer. In contrast, anodization layer 600 is substantially opaqueand generally does not allow an unobstructed view of underlying aluminumsubstrate 612.

It should be noted that conventional methods for forming a transparentanodization layer require that the anodization layer be thin, forexample 2 to 3 microns, in order to maintain a transparent quality.However, such a thin anodization layer is more susceptible to damagesuch as scratching. An advantage of embodiments presented herein is thata transparent anodization layer can be formed to approximate thethickness and scratching resistance of an adjacent opaque anodizationlayer while providing a transparent quality normally associated withthinner anodization films. In addition, the transparent anodizationlayer described herein can be significantly harder than a layer of 2-3micron anodized film using a conventional anodizing process. Thesefeatures are illustrated in FIGS. 7A and 7B, which show selected sideview profiles of two parts, 700 and 720 that have undergone differentanodizing processes. FIG. 7A shows part 700 which has undergone aconventional anodizing process using standard processing parameters,forming opaque anodization layer 704 that has a thickness 706 of about 8to 12 microns. Part 700 has also undergone another conventionalanodizing process to form adjacent anodization layer 708 which hasthickness 710 of about 2 to 3 microns. Anodization layer 708 issubstantially transparent, revealing underlying metal 702. However, therelative low thickness of anodization layer 708 can make it morevulnerable to scratching and damage that may occur during, for example,normal use of an electronic device. In addition, the thicknesses ofadjacent anodization layers 704 and 708 differ by about 5 to 10 microns,which can allow debris, such as dirt, grease and other particles, toform at the interface 728 of the thinner anodization layer 708 andthicker first anodization layer 704 during normal use of an electronicdevice.

FIG. 7B shows part 720 which has undergone a different anodizing processthan part 700 in FIG. 7A. Part 720 has undergone a conventionalanodizing process using standard processing parameters, forming opaqueanodization layer 724 that has a thickness 706 of about 8 to 12 microns.Part 720 has additionally undergone an anodizing process using processparameters in accordance with described embodiments to form adjacenttransparent anodization layer 726. Because layer 726 is transparent,underlying surface features of metal 722 are viewable from the topsurface of transparent layer 726. Transparent anodization layer has athickness 728 of about 7 to 9 microns, a relatively large thicknesscapable of withstanding normal wear during normal use of an electronicdevice. In addition, the thicknesses of adjacent anodization layers 724and 726 differ by about 0 to 5 microns, which reduces the likelihood fordebris to form at the interface 730 between the two anodization layersduring normal used of an electronic device. In addition, since thethickness of transparent anodization layer 726 approximates thethickness of adjacent anodization layer 724, the overall top surface ofthe anodization layers is more uniform, smooth and aestheticallyappealing.

In some embodiments, the anodizing process for forming a transparentanodization layer includes a slow ramp up procedure wherein theanodizing current density or voltage is slowly ramped up to a targetanodizing current density or voltage used for bulk film growth. FIG. 8is a graph showing current change as a function of time for a slowcurrent ramp up procedure in accordance with the described embodiments.FIG. 8 shows that in a more conventional current density or voltage rampup 802, the current density or voltage increases quickly over time totarget anodizing current density or voltage 804. In this case, currentdensity or voltage ramp up 802 increased to the target current densityor voltage over a period of 0.5 minutes. For example, if the targetanodizing current density 804 is 1.5 Amps/dm², in a standard ramp upprocedure the current density would be ramped up from 0 Amp/dm² to 1.5Amps/dm² over a 0.5 minute period. In a slow ramp up 806, in accordancewith certain embodiments, the current density or voltage is increased ata much slower pace to target current density or voltage 804, forexample, over at least about a 5 minute period. For example, if thetarget anodizing current density 804 is 1.5 Amps/dm², in a slow ramp upprocedure the current density would be ramped up from 0 Amp/dm² to 1.5Amps/dm² over at least a 5 minute period. It is believed that the slowercurrent density or voltage ramp up results in the formation of a moreuniform barrier layer which promotes growth of a more uniform bulkanodization layer thereon, and therefore more conducive to forming atransparent bulk anodization layer thereon.

FIGS. 9A-9C illustrate top down views of a part 900 with a portion ofmetal surface undergoing an anodizing process which involves a slow rampup procedure as describe above with reference to FIG. 8. In FIG. 9A, atthe beginning of the slow ramp up procedure (t0), anodization materialstarts to form at nucleation sites 904 on metal surface 902. At FIG. 9B,the slow ramp up has proceeded for a time (t1) and anodization material906 has slowly grown outward from nucleation sites 904. At FIG. 9C, theslow ramp up has proceeded for a longer time (t2) and anodizationmaterial has grown outward from nucleation sites 904 to the point thatanodization material such that anodization material completely cover thesurface of metal surface 902, thereby forming barrier layer 908. Becausethe current density or voltage is allowed to ramp up slowly, for exampleduring about a 5 minute period, the anodization film grows more slowlyand uniformly around nucleation sites 904, thus providing a more uniformbarrier layer 908. The ramp up time period is preferably at least about5 minutes. Once barrier layer 908 has been formed, the current densityor voltage can then be maintained at a target current density or voltageto continue bulk anodization film growth. It is believed that theformation of a uniform barrier layer promotes a more uniform bulkanodization film growth thereon, resulting in a overall uniform and moretransparent final anodization layer. Note that the slow ramp procedurecan involve the slow ramp up of current density or voltage to a targetcurrent density or voltage.

FIG. 9D is a flow chart illustrating details of a process for forming abarrier layer and transparent anodization film in accordance withdescribed embodiments. At 910, a barrier layer is formed on an aluminumsubstrate using a slow ramp up procedure as described above. Asdescribed previously, some embodiments can involve the slow ramp up ofcurrent density and other embodiments involve the slow ramp up ofvoltage. The resultant barrier layer is uniform and can promote uniformanodization film growth thereon. The barrier layer is sufficiently thinas to provide an unobstructed view of the underlying aluminum substrate.At 920, a transparent anodization film is disposed directly on thebarrier layer using the process parameters described above (FIG. 6B,anodization layer 606). The resulting transparent anodization layer haspores that are sufficiently small in diameter and sufficiently denselypacked so as to provide light transmission through the transparentanodization layer from the top surface of the anodization layer to thetop surface of barrier layer. Since the barrier layer does notsubstantially obstruct transmission of light, a viewer can be permitteda substantially unobstructed view of a surface feature on the aluminumsubstrate. As described above, although the transparent anodizationlayer can provide a substantially unobstructed view of an underlyingsubstrate, it can be formed at a thickness to maintain a high resistanceto wear such as scratching.

As described above, embodiments described herein are suitable forproviding a cosmetically appealing and protective anodization layer onangled metal surfaces, such as the chamfered surfaces 30 a and 30 bshown in FIG. 2. In conventional methods, a single anodization layer istypically formed on a metal surface, including portions of the metalsurface having angles and corner. Embodiments described herein provide adouble anodization process whereby at least two separate anodizationlayers are formed on different portions of the angled metal surface,thereby creating a more uniform and appealing appearance at the anglededges and corners. To illustrate, FIG. 10A shows a selected profile of apart 1000 having edges 1018 which has undergone a single anodizingprocess, thereby forming anodization layer 1002 on metal substrate 1016.It should be noted that for simplicity, FIG. 10A does not show a barrierlayer or location of the metal surface prior to anodizing (such as thoserepresented by dashed lines in FIGS. 5A-5D). As shown in the inset view,anodization layer 1002 has irregular cracks 1004 that meander betweenthe side surfaces and top surface of the edges 1018. When viewed from ahigh level perspective, meandering cracks 1004 reflect light and becomevisible at different angles depending on whether the crack is on theside surfaces or top surface of the angled regions. The result isblurred features on part 1000 that appear as an uneven edge highlightswhich are not aesthetically appealing.

In embodiments described herein, a process involving two anodizingprocedures is performed on angled surfaces to provide an aestheticallyappealing protective layer. Suitable surfaces include a housing ofconsumer electronic product such as the portable electronic device ofFIGS. 2 and 3. In some embodiments the consumer electronic product has asingle piece metal housing having top and bottom portions with sidewalls. The consumer electronic product can have a front openingsurrounded and defined by the top portion. The bottom portion and sidewall can cooperate with the top portion to form a cavity in cooperationwith the front opening. In some embodiments, a chamfered portion isdisposed between the top portion and a side wall. Described embodimentscan be used for providing a protective anodization layer on top andbottom portions, side walls and chamfered portion of the consumerelectronic product.

To illustrate, FIGS. 10B-10E show selected profiles of a metal surface,such as the edge of an electronic device housing, undergoing a doubleanodizing process. At FIG. 10B, metal part 1020 has first surface 1022,having a first surface orientation vector 1026 which is orthogonal tofirst surface 1022, and second surface 1024, having a second surfaceorientation vector 1028 which is orthogonal to second surface 1024. Notethat first 1026 and second 1028 surface orientation vectors arereference vectors for surfaces 1026 and 1024, respectively, and notintended to show overall direction of subsequent oxide growth. At FIG.10C, primary anodization layer 1030 is grown on a selected portion ofmetal part 1020 that includes first 1022 and second 1024 surfaces. Itshould be noted that for simplicity, FIGS. 10C-10E do not show barrierlayers or locations of the metal surfaces prior to anodizing (such asthose represented by dashed lines in FIGS. 5A-5D). At FIG. 10D, acontiguous portion of primary anodization layer 1030 and a correspondingpre-determined amount of underlying metal housing are removed to formchamfered assembly 1032. In some embodiments, the removing involvescutting metal part 1020 using a cutter. In some embodiments, the cuttingprovides a mirror reflective surface. In some embodiments, removing caninvolve a laser and/or etch procedure. Chamfered assembly 1032 includesthird surface 1034 having a third surface orientation vector 1036 whichis orthogonal to third surface 1034. Third surface 1034 is contiguouswith and disposed between remaining portions 1038 and 1040 of first 1022and second 1024 surfaces.

At FIG. 10E, a secondary anodization layer 1042 is grown on thirdsurface 1034 in accordance with third surface orientation vector 1036.Note that third surface orientation vector 1036 is a reference vectorfor surface 1034 and not intended to show overall direction ofsubsequent oxide growth. In some embodiments, the secondary anodizationlayer and primary anodization layers have different properties, such aspore density and average pore size as described above with reference toFIGS. 6A and 6B. Because of the nature of an anodizing process,secondary anodization layer 1042 grows in a substantially orthogonaldirection with respect to third metal surface 1034. Secondaryanodization layer 1042 grows substantially only on exposed metalsurfaces such as third surface 1034. Since anodizing is generally aconversion process where a portion of metal part 1020 is converted to anoxide, secondary anodization layer 1042 is shown to grow inward with aportion of secondary anodization layer 1042 that extends above thirdsurface 1036. Secondary anodization layer 1042 includes first edge 1044adjacent to remaining portion 1038 and second edge 1046 adjacent toremaining portion 1040. First 1044 and second 1046 edges align withthird orientation vector 1036 such that a first angle 1048 between firstedge 1044 and remaining portion 1038 of the first surface is about equalto a second angle 1050 between second edge 1046 and remaining portion1040 of the second surface. Thus, the interfaces between secondaryanodization layer 1042 and primary anodization layer 1030 are regularand well defined which from a high level perspective appear as neatlines that are cosmetically appealing. It should be noted that thethickness of secondary anodization layer 1042 can closely approximatethe thickness of primary anodization layer 1030, thus providing anoverall smooth quality at the angled metal region of part 1020. In someembodiments, the difference in thickness between primary 1030 andsecondary 1042 anodization layers is about 5 microns or less. Thus, thedescribed embodiments can be used to form smooth and aestheticallypleasing anodization layers on edged surfaces.

In addition to forming regular and well defined lines at edged metalsurfaces, certain embodiments can provide an enhancing highlight effectat the interface between a primary anodization layer and secondaryanodization layer. FIGS. 11 and 12A-12F illustrate steps involved in ahighlighting process wherein a highlighted boundary is formed betweentwo anodization layers in accordance with described embodiments. FIG. 11is a flowchart showing process steps. FIGS. 12A-12F are graphical sideviews of a portion of a part undergoing the process described in FIG.11. In the following narrative, reference will be made to both theflowchart of FIG. 11 in conjunction with the side view presentations ofFIGS. 12A-12F.

Process 1100 begins at 1102 (corresponding to FIG. 12A) where a maskingoperation is performed on metal piece 1200 having a first surface 1202and second surface 1204, forming mask 1206 on second surface 1204. Themask can be any suitable mask capable of withstanding a subsequentblasting and anodizing process. In some embodiments, a photoresist maskis used, wherein the photoresist has a pattern. First 1202 and second1204 surfaces are adjacent and contiguous with each other. At 1104(corresponding to FIG. 12B), a texture 1208 is created on first metalsurface 1202. Texture 1208 can be, for example, a rough or “blasted”surface created from a blasting operation. The blasting operation caninclude, for example, exposing the metal piece to a blasting media suchas zirconia applied under pressure (e.g., 1 bar). At 1106 (correspondingto FIG. 12C), mask 1206 is treated so as to decrease the adhesion of theedges 1210 of mask 1206, exposing an untextured portion 1212 of secondsurface 1204 adjacent to the blasted metal surface 1208. In this way,edges 1210 of mask 1206 adjacent to the textured 1208 first metalsurface 1202 are lifted off the underlying second metal surface 1204.Treatment of the mask can include a chemical rinse using, for example, adilute acid solution. Alternatively, a laser ablation procedure can beused to remove edges of the mask material. In some cases, edges of themask may become naturally less adhesive to the metal surface duringexposure to anodizing processes.

At 1108 (corresponding to FIG. 12D), a first anodizing process isperformed creating a primary anodization layer 1214 on blasted metalsurface 1208 and exposed untextured metal portion 1212. Primaryanodization layer 1214 is hazy and does not clearly reveal the surfaceof underlying metal 1200. At 1110 (corresponding to FIG. 12E), mask 1206is removed, exposing the remaining un-anodized second surface 1204.Second surface 2104 has retained any previously provided surfacefeatures such as artwork or reflectiveness. At 1112 (corresponding toFIG. 12F), a second anodizing process is performed creating a secondaryanodization layer 1216 on a second surface 1204. Primary 1214 andsecondary 1216 anodization layer can have different physical andmicro-structure properties. For example, secondary anodization layer1216 can be substantially clear to reveal any features such as artworkor reflectiveness of the underlying metal 1200 while primary anodizationlayer 1214 can be substantially opaque. In this case, finished part 1218has a textured surface 1208 with an opaque primary anodization layer1214, an adjacent untextured portion 1220 which is opaque, and secondaryanodization layer 1216 which is substantially transparent with anuntextured surface 1222. Thus, visually, untextured surface 1220 can actas a highlight region or highlighted boundary that surrounds and definessecondary anodization layer 1216, which is transparent and revealsunderlying metal 1200. It should be noted that although FIGS. 12A-12Fillustrate a flat metal piece 1200, the highlighting methods describedherein can be used on substrates with angled features, such as metalpart shown in FIGS. 10B-10E. In these cases, methods provided herein canprovide a consistent highlight along the edges of the part.

Use of Photomasks Having Pre-Distortion Features

As mentioned above, in some embodiments a photomask used to form thephotoresist that covers artwork can include pre-distortion features inorder to provide sharply defined corners in the resulting artwork. Ingeneral, a photomask is an opaque plate with holes or transparenciesthat allow light to shine through in a defined pattern. When the definedpattern of light shines on a layer of photoresist covering a substrate,the photoresist will take on the defined pattern. If a positive typephotoresist is used, the portion of the photoresist that is exposed tolight becomes soluble to the photoresist developer. The portion of thephotoresist that is unexposed remains insoluble to the photoresistdeveloper and remains on the surface of the substrate. If a negativetype photoresist is used, the portion of the photoresist that is exposedto light becomes insoluble to the photoresist developer. The unexposedportion of the photoresist is dissolved by the photoresist developer.

Corner regions of the underlying photoresist tend to be overexposed orunderexposed to light depending on whether the corner is an exteriorcorner or an interior corner. The underexposed or overexposed cornerregions of the photoresist in turn result in these corner regions beingunderdeveloped or overdeveloped, respectively, in the photoresistdeveloper. When the pattern is transferred onto the substrate, thecorners will appear rounded and no longer sharp. In embodimentsdescribed herein, the photoresist can be exposed to not only aphotolithography process, but also a blasting process and/or ananodizing process. The pre-distortion features in accordance withdescribed embodiments can reduce the amount of corner rounding that canbe caused by a photolithography process as well as a subsequent blastingand/or anodizing process.

In a blasting process, the photoresist, which is generally made of arelatively soft material, can be exposed to a physically harshenvironment since the blasting media has abrasive particles appliedunder pressure. Corner regions of a pattern on the photoresist areespecially susceptible to erosion from the blasting media, resulting ina pattern on the metal having rounded corners. It should be noted thatin order to withstand the physically harsh environment of a blastingprocess, the photoresist is preferably relatively thick. Corner roundingcan be further exacerbated if the photoresist is thick since it can bedifficult for the light to penetrate though the entire thickness of thephotoresist material. In addition, photoresist material generallybecomes softer the thicker it is applied, thereby making it morevulnerable to damage from subsequent procedures such as blasting. Afterthe photoresist is removed, the metal surface can then exposed to ananodizing process to form a protective anodization layer on the metalsurface. If an anodizing procedure is used, the anodizing process canfurther round the appearance of the edge and corner features. This isbecause the anodizing process adds an additional layer onto the metalsurface which can distort the appearance of and erode the sharpness ofedges and corners of the pattern in the underlying metal surface.

In order to compensate for the above mentioned corner rounding effects,embodiments described herein include methods for providing a photomaskwith pre-distortion features at the corner regions of a photolithographypattern to provide a desired resultant pattern with sharply definedcorners on the substrate. The pre-distortion regions on the photomaskpattern appear as tapered portions extending from exterior corners andrecessing within interior corners of the pattern.

FIGS. 13A-13B and 14A-14D depict close-up top-down views of photomaskpatterns and resultant corresponding photoresist patterns on substratesusing photomasks having pre-distortion features in accordance withdescribed embodiments. In FIG. 13A, photomask 1300 is configured fordeveloping negative type photoresist. A pattern having opaque portion1304 and transparent portion 1302 is disposed on photomask 1300. Duringthe photolithography process, light is shone through transparent portion1302 onto a layer of negative photoresist which is disposed on asubstrate. The exposed portions of the negative photoresistcorresponding to the transparent portion 1302 will remain on thesubstrate while unexposed portions of the negative photoresistcorresponding to opaque portion 1304 will be dissolved and removed bythe photoresist developer. As shown, transparent portion 1302 hasextending pre-distortion feature 1310 positioned at exterior corner 1306and receding pre-distortion feature 1312 at interior corner 1308.Extending pre-distortion feature 1310 compensates for the tendency ofthe underlying photoresist corresponding to exterior corner 1306 to beunderexposed to light during the photolithography process and fordegradation during subsequent blasting and/or anodizing processes. Thus,extending pre-distortion feature 1310 reduces the amount of cornererosion that can be caused by subsequent blasting and/or anodizingprocesses. Receding pre-distortion feature 1312 compensates for thetendency of the underlying photoresist corresponding to interior corner1308 to be overexposed to light during the photolithography process andfor degradation during subsequent blasting and/or anodizing processes.Thus, receding pre-distortion feature 1312 reduces the amount of cornererosion that can be caused by subsequent blasting and/or anodizingprocesses.

In FIG. 13B, photomask 1318 is configured for developing positive typephotoresist. A pattern having opaque portion 1322 and transparentportion 1324 is disposed on photomask 1318. During the photolithographyprocess, light is shone through transparent portion 1324 onto a layer ofphotoresist which is disposed on a substrate. The exposed portions ofthe positive photoresist corresponding to the transparent portion 1324will be dissolved and removed by the photoresist developer whileunexposed portions of the positive photoresist corresponding to opaqueportion 1322 will remain on the substrate. As shown, transparent pattern1324 has extending pre-distortion feature 1330 positioned at exteriorcorner 1328 and receding pre-distortion feature 1320 at interior corner1326. Extending pre-distortion feature 1330 compensates for the tendencyof the underlying photoresist corresponding to exterior corner 1328 tobe underexposed to light during the photolithography process and fordegradation during subsequent blasting and/or anodizing processes. Thus,extending pre-distortion feature 1330 reduces the amount of cornererosion that can be caused by subsequent blasting and/or anodizingprocesses. Receding pre-distortion feature 1320 compensates for thetendency of the underlying photoresist corresponding to interior corner1326 to be overexposed to light during the photolithography process andfor degradation during subsequent blasting and/or anodizing processes.Thus, receding pre-distortion feature 1320 reduces the amount of cornererosion that can be caused by subsequent blasting and/or anodizingprocesses.

FIGS. 14A-14D illustrate a photomask, photoresist and substrate atdifferent stages of processing in accordance with described embodiments.In the embodiments depicted in 14A-14D, a negative type photoresist isused. It should be noted that methods described herein with respect tonegative type photoresist can also be used for positive typephotoresists. At FIG. 14A, photomask 1400 has opaque portion 1402 withtransparent pattern 1404 formed therein. Transparent pattern 1404 hasextending pre-distortion feature 1406 at exterior corners and recessingpre-distortion feature 1408 at interior corners. FIG. 14B, showssubstrate 1410 after a photolithography process has been performed usingphotomask 1400. In a photolithography process, a UV light is shonethrough the transparent pattern 1404 to form a corresponding pattern ona photoresist that has been spun onto an underlying substrate. It shouldbe noted that since the photoresist will undergo a subsequent blastingprocess, the photoresist material is preferably applied on to arelatively thick layer. In some embodiments, the photoresist is betweenabout 40 to 50 microns thick. The photoresist is then developed toremove unexposed portions of the photoresist, leaving patternedphotoresist 1414 and exposed substrate portion 1412. As shown in theinset view, portions of the extending 1406 and receding 1408pre-distortion features from the transferred pattern of photomask 1400have been rounded by the time the pattern was transferred to photoresist1414. This corner rounding is caused by optical effects of thephotolithography process wherein corner regions in a photomask patterntend to be underexposed and overexposed during a photolithographyprocess, as described above. As a result, patterned photoresist 1414 hasa first photoresist feature 1416 at outside corners and a secondphotoresist feature 1418 at inside corners. First photoresist feature1416 and second photoresist feature 1418 of the photoresist are roundedand less pronounced as the extending 1406 and receding 1408pre-distortion feature of photomask 1400.

FIG. 14C shows substrate 1410 after undergoing a blasting process. Asmentioned above, a blasting process involves the use of an abrasivematerial that impinges upon the substrate at a certain pressure in orderto achieve a textured surface on portions of the substrate unprotectedby photoresist. In one embodiment, the blasting media takes the form ofzirconia applied under pressure. Since photoresist material is generallyrelatively soft, some of the photoresist material can be displaced andremoved by the impinging particles during the blasting process,especially at exterior corners of the photoresist layer, resulting inrounded protruding corners. At interior corners of the photoresistlayer, blobs of photoresist can form due to the displacement anddislodgment of photoresist material, resulting in rounded interiorcorners. If the photoresist material is too thin, blasting can formholes in the photoresist material which can lead to damage to underlyingportions of the substrate. However, if the photoresist layer is toothick, the entire thickness of the photoresist may not be sufficientlyexposed to UV light during the photolithography process, thereby furtherexacerbating the rounding effects described above. Optimized thicknessesof photoresist can depend upon a number of factors such as the type ofphotoresist material used and UV wavelengths and intensities used. It isnoted than any suitable photoresist material that can withstand aphotolithography process, a blasting process and/or an anodizationprocess can be used. The photoresist can be applied on the substrateusing any suitable technique, such as a spray coating or spin onoperation.

Returning to FIG. 14C, after substrate 1410 is exposed to a blastingprocess, resultant substrate 1420 has textured portion 1422 andpatterned photoresist 1424 which protects an underlying portion ofsubstrate. As shown in the inset view, portions of first photoresistfeature 1416 and second photoresist feature 1418 prior to blasting havebeen eroded by the blasting media. As a result, patterned photoresist1424 has first photoresist feature 1426 at exterior corners and secondphotoresist feature 1428 at interior corners, respectively, which arerounded and less pronounced compared to first photoresist feature 1416and second photoresist feature 1418 of the photoresist prior to theblasting process.

FIG. 14D shows substrate 1420 after photoresist 1424 has been removedand the metal surface has undergoing an anodizing process. As mentionedabove, an anodizing process can further round or distort the sharpnessof corners since an anodization layer adds a layer of material over thesubstrate. In FIG. 14D, after substrate 1420 is exposed to ananodization process, resultant substrate 1430 has textured anodizedportion 1432 and untextured anodized portion 1434. As shown in the insetview, untextured anodized portion 1434 has sharply defined exteriorcorner 1436 and sharply defined interior corner 1438. If protruding andindenting corners of photomask 1400 did not have the extending 1406 andreceding 1408 pre-distortion features, the resulting photoresist 1434after photolithography, blasting and anodizing processes would berounded and less aesthetically appealing. Thus, the extending 1406 andreceding 1408 pre-distortion features in photomask 1400 compensate forcorner erosion that occurs caused by the subsequent blasting processexperienced by photoresist 1424 and further for corner rounding causedby the subsequent anodizing process.

FIG. 14E is a flow chart illustrating details of a process for forming apattern on a substrate using a photomask with pre-distortion features inaccordance with described embodiments. At 1450, a pattern is formed on aphotoresist disposed on a substrate, the pattern formed by a photomaskhaving a pattern with a first pre-distortion feature and/or a secondpre-distortion feature at exterior and/or interior corners,respectively. As described above, the first pre-distortion featureextends from the exterior corners and the second pre-distortion featurerecedes within the interior corners. At 1452, the substrate is exposedto a photolithography process to form a photoresist having acorresponding pattern of the photomask on the substrate. At 1454, thesubstrate undergoes a blasting process to form a textured surface onportions of the substrate that are unprotected by the photoresist. Nextat 1456, the photoresist is removed to form a pattern on the substratehaving textured and un-textured portions. At 1458, the substrateundergoes an anodizing process to form an anodized layer on the texturedand un-textured pattern. The resultant anodized and blasted surface willhave sharply defined and aesthetically appealing corners.

Molding Techniques for Anodizing Resistant Components

As discussed above, certain structural portions of an electronic devicecan be formed from plastic or resin materials in accordance withdescribed embodiments. The plastic portions can be configured towithstand exposure to harsh manufacturing processes and chemicals, suchas those encountered during an anodizing process. As described below,the plastic structural portions can be integrated into the housing of anelectronic device using a two-shot molding process. FIGS. 15A-15B and 16show several illustrative views of an electronic device which includeplastic portions in accordance with some embodiments. FIGS. 15A-15B showouter periphery component 100 that can be constructed by connectingseveral sections together, such as sections 110, 120, and 130. In someembodiments, outer periphery component 100 can be constructed byconnecting section 110 and section 120 together at interface 112, andconnecting section 120 and section 130 together at interface 122. Tomechanically couple individual sections together, coupling members 114and 124 can exist at interfaces 112 and 122, respectively. Couplingmembers 114 and 124 can be constructed from an injection molding processwherein the plastic that begins in a first, liquid state and thensubsequently changes to a second, solid state. Upon changing into thesolid state, the plastic material can then bond together sections 110and 120, and 120 and 130, respectively, thus forming a single newcomponent (e.g., outer periphery component 100). Coupling members 114and 124 can not only physically couple together sections 110 and 120,and 120 and 130, respectively, they can also electrically isolatesection 110 from section 120, and section 120 from section 130.

Coupling members 114 and 124 can exist with integrally formed lockingstructures that are attached to or integrally formed with parts ofsections 110, 120, and 130. A shutoff device (not shown) may bepositioned at each interface to shape the coupling member for when ittransforms into its second state (e.g., the solid state). Couplingmembers 114 and 124 are constructed to span a width of outer peripherymember 100, as shown. A portion of the coupling members 114 caninterface with locking members 141-155 existing on the sidewalls ofsections 110, 120, and 130, and other portions of members 114 and 124can interface with additional locking members existing on the edge ofthe sections. When coupling member 114 is applied in a liquid state, itflows into and/or around locking members 141-155, and as it turns into asolid, it forms a physical interconnect that couples sections 110 and120 together. Coupling member 114 can include screw inserts that line upwith holes in section 110 so that screws or other fastener can be usedto secure section 110 to member 114.

Coupling members 114 and 124 may be machined, for example, after it isapplied as a first shot, so as to have holes, recesses, retentionfeatures, or any other desired features. Some machined features areillustratively as elements 161-167. For example, elements 161-163 areholes, and elements 165-167 are rectangular cutouts. These machinefeatures can enable cables to pass from one side of the coupling memberto another or to enable secure placement of various components such as abutton, a camera, a microphone, a speaker, an audio jack, a receiver, aconnector assembly, or the like. Coupling members 114 and 124 can beconstructed to include a first shot component and a second shotcomponent. The first and second shot components can be composed ofdifferent materials, wherein the first shot is composed of a relativelyhigher strength structural material than the second shot material. Thefirst shot component can be responsible for the physical coupling of thesections (e.g., section 110 to section 120) and can be machined toinclude retaining regions for receiving the second shot.

The first shot can be formed by an injection molding process wherein theplastic begins in a first liquid state and subsequently changes to asecond solid state. While in the liquid state, the plastic can beallowed to flow into interfaces 112 and 122 and in locking members141-155. After flowing into the interfaces locking members, the plasticmaterial can subsequently be allowed to harden (e.g., the plasticmaterial is allowed to change into the second solid state). The secondshot component can serve as a cosmetic component that is self-anchoredwithin the retaining region of the first shot. The second shot can beformed by injection molding the plastic onto at least a portion of thesurface of the first shot component. The second shot can be formedwithin cavities of the first shot that serve as mechanical interlocksthat physically couple the first and second shots together. Afterflowing into portions of the first shot, the plastic material cansubsequently be allowed to harden. In certain embodiments, the secondshot is only formed on portions of the surface of the first shot thatwould otherwise be visible from the outside of the electronic device. Inthese cases, the second shot can be the only part that is visible to theuser when the device is fully assembled. In some embodiments, the secondshot is formed to take up as little space as possible in the devicewhile still providing adequate coverage for cosmetic purposes. In someembodiments, the second shot completely surrounds and protects the firstshot. In some cases the second shot can be as thin as a veneer which canpartially or completely surrounds the surface of the first shot.

During the injection molding process, while in liquid state, the secondshot is allowed to flow into and/or around locking structures formedwithin the first shot component. The second shot can have any suitablecolor. As shown in FIGS. 15A-15B, coupling members 114 and 124 are shownto include first shot component 430 and second shot component 440. Firstshot component 430 includes interface features for interfacing withlocking mechanisms of sections 120 and 130. First shot component 430 canalso include second shot retention regions for receiving second shotcomponents 440. FIG. 16 shows a close up view of sections 110 and 120with second shot component 440 disposed there between. In someembodiments, second shot component 440 is visible and first shotcomponent 430 is not visible from the exterior of the component 100.

Coupling members 114 and 124 can be exposed to various physically andchemically harsh environments during the manufacturing process. Forexample, the side walls and back plate of an electronic device canundergo polishing or lapping operations, which can involve the use ofvery acidic (e.g., around pH 2) and/or very alkali (e.g., around pH 8-9)slurries depending on whether the polishing is a fine or a roughpolishing procedure. In addition, during photolithograph, the device canbe exposed to UV light during UV curing stage and developing stage, aswell as exposure to a strong base such as sodium hydroxide for rinsingaway non-cured photoresist material. Furthermore, during an anodizingprocess, the device can be subjected to a variety of acidic and alkalisolutions at elevated temperatures and for extended amounts of time, asdescribed above with reference to anodizing techniques. If a blastingprocedure is used, the plastic material can be exposed to a pressurizedblasting media. In one embodiment, the blasting media takes the form ofzirconia applied under about 1 bar of pressure. Additionally, duringde-masking (used to remove photoresist material) the device can beexposed to acidic or alkali rinses solutions at elevated temperatures.Moreover, during a CNC the device can be exposed to cutting fluids. Thefirst shot and second shot materials can be unaffected by one or more ofthe above described processes in that they can maintain structuralintegrity and can appear substantially unmarred. It should be noted thatin some embodiments a mask can be used to prevent degradation ofportions of plastic during some of the processes described above. Forexample, a mask can be used to protect plastic during higher intensityUV exposure during photolithography and during certain CNC steps toprotect the plastic surface from scratching. Any suitable mask toprotect the plastic can be used. In one embodiment, a UV curable polymermask is used.

In embodiments described herein the plastic materials used forfabricating portions, such as coupling members 114 and 124, can beconfigured to withstand the physical and chemical conditions of one ormore of the above described processes. The first and second shot can bemade of different materials to serve different purposes. In someembodiments, the first shot can be made of a stronger material so as toprovide structural support for the electronic device and the second shotcan be made of a softer but more cosmetically appealing material foraesthetic purposes. In certain embodiments, both the first shot andsecond shot materials are configured to withstand the physical andchemical conditions of one or more of the above described processes. Inembodiments where the second shot completely surrounds the first shot,the second shot can be resistant to one or more of the above describedprocesses while the first shot is not necessarily resistant to one ormore of the above described processes. That is, the second shot canprotect the surface of the first shot from the subsequent processes. Inone embodiment, the first shot material is made of a high mechanicalstrength thermoplastic polymer resin such as a glass filledpolyaryletherketone (PAEK) material. In other embodiments a glass filledpolyethylene terephthalate (PET) material is used. In preferredembodiments, the second shot appears as smooth and even, therebyproviding a more cosmetically appealing appearance than the first shot.In some cases, the second shot can take on one of more colors.

FIG. 17 is a flowchart illustrating details of process for forming atwo-shot plastic member for an enclosure that is resistant to ananodizing process in accordance with described embodiments. At 1710, afirst shot component of a plastic member of an enclosure is formed, thefirst shot component being made of a high strength structural materialthat is resistant to a subsequent anodizing process. At 1720, a secondshot component of the plastic member of an enclosure is formed, thesecond shot component formed to cover at least part of the surface ofthe first shot component. The second shot component material is made ofa different material than the first shot component and is resistant to asubsequent anodizing process. As described above, in some embodiments,the first shot and second shot material can be resistant to a subsequentprocess such as polishing, UV photolithography, blasting de-masking orCNC process. The first and second shot components can be formed byinjection molding process, as described above, wherein they are each ina first liquid state and harden to a second solid state.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of specific embodimentsare presented for purposes of illustration and description. They are notintended to be exhaustive or to limit the described embodiments to theprecise forms disclosed. It will be apparent to one of ordinary skill inthe art that many modifications and variations are possible in view ofthe above teachings.

What is claimed is:
 1. A method of forming a multi-part enclosure for anelectronic device, the multi-part enclosure including at least a firstmetal section and a second metal section, wherein the multi-partenclosure is characterized as having a width that extends betweenexterior surfaces of opposing sidewalls of the first and second metalsections, the method comprising: locking together the first metalsection and the second metal section in a locked configuration byinjection molding a first shot component comprised of a first liquidmaterial into recessed locking members included in the first and secondmetal sections, wherein the recessed locking members span the width ofthe multi-part enclosure such that the first liquid material hardens toform a coupling member that locks with the recessed locking members soas to electrically isolate the first metal section from the second metalsection, wherein in the locked configuration, a surface of the firstshot component is unprotected from an anodization process performed atthe exterior surfaces of the opposing sidewalls; injection molding asecond shot component comprised of a second liquid material to cover andprotect at least the surface of the first shot component from theanodization process performed at the exterior surfaces of the opposingsidewalls subsequent to the injection molding of the second shotcomponent; performing the anodization process at the exterior surfacesof the opposing sidewalls corresponding to the second shot component,wherein the first shot component is protected from the anodizationprocess by the second shot component; and machining the coupling memberto form a recess that is capable of carrying an electronic componenttherein.
 2. The method recited in claim 1, wherein the multi-partenclosure is characterized as having a height that extends between a topsurface of the first metal section and a bottom surface of the secondmetal section, and the height is greater than the width.
 3. The methodrecited in claim 1, wherein the second shot component completely coversthe first shot component and includes an exterior surface that is flushwith the exterior surfaces of the opposing sidewalls.
 4. The methodrecited in claim 1, wherein the first and second liquid materials areplastic material.
 5. The method recited in claim 1, wherein the recessedlocking members are included at the opposing sidewalls of the first andsecond metal sections.
 6. The method recited in claim 1, wherein thesecond shot component is self-anchored within a cavity that is filled bythe first shot component.
 7. The method recited in claim 1, wherein,subsequent to injection molding the second shot component, the firstshot component is completely surrounded by the second shot component. 8.The method recited in claim 1, wherein the first shot component iscomprised of a thermoplastic polymer resin.
 9. The method recited inclaim 1, wherein the first shot component is comprised of glass filledpolyaryletherketone (PAEK) material or polyethylene terephthalate (PET)material.
 10. The method recited in claim 1, wherein the second liquidmaterial in a hardened state is softer than the first liquid material ina hardened state.
 11. The method recited in claim 1, wherein themulti-part enclosure further includes a third metal section, and therecessed locking members span the width of the third metal section. 12.A method for forming a multi-part enclosure, the multi-part enclosureincluding at least a first metal section and a second metal section,wherein the multi-part enclosure is characterized as having a width thatextends between opposing sidewalls of the first and second metalsections, the method comprising: locking together the first metalsection with the second metal section by injection molding a first shotcomponent into recessed locking members of the first and second metalsections, the first shot component being comprised of a first material,wherein the recessed locking members span the width of the multi-partenclosure such that when the first shot component hardens to form acoupling member, the first and second metal sections are locked togetherand electrically isolated from each other by the coupling member;injection molding a second shot component to cover any exposed surfacesof the first shot component, the second shot component comprised of asecond material that is different than the first material and isresistant to an anodization process; anodizing exterior surfaces of theopposing sidewalls, wherein the second shot component protects the firstshot component from the anodization process; and machining the couplingmember to form a recess that is capable of carrying an electroniccomponent therein.
 13. The method recited in claim 12, wherein themulti-part enclosure is characterized as having a height that extendsbetween a top surface of the first metal section and a bottom surface ofthe second metal section, and the height is greater than the width. 14.The method recited in claim 12, wherein the recessed locking memberscorrespond to the opposing sidewalls of the multi-part enclosure. 15.The method recited in claim 12, wherein the first shot component iscomprised of a thermoplastic polymer resin, a glass filledpolyaryletherketone (PAEK) material or a polyethylene terephthalate(PET) material.
 16. A method of forming a multi-part enclosure for anelectronic device, the multi-part enclosure including at least a firstmetal section and a second metal section, wherein the multi-partenclosure has a width that extends between exterior surfaces ofsidewalls of the first and second metal sections, the method comprising:locking together the first metal section with the second metal sectionby injection molding a first shot component at recessed locking membersof the first and second metal sections, wherein the recessed lockingmembers extend along the width of the multi-part enclosure such thatwhen the first shot component hardens to form a coupling member, thefirst and second metal sections are locked together and electricallyisolated from each other by the coupling member; machining the firstshot component to form retaining features that includes a lockingstructure capable of accepting a second shot component; injectionmolding the second shot component into the locking structure such thatthe second shot component is self-anchored to the first shot component,wherein the second shot component prevents the first shot component frombeing viewable and protects the first shot component from an anodizationprocess; and machining the coupling member to form a recess that iscapable of carrying an electronic component therein.
 17. The methodrecited in claim 16, wherein the multi-part enclosure further includes athird metal section, and the first and third metal sections areseparated by the second metal section.
 18. The method as recited inclaim 17, wherein the multi-part enclosure is characterized as having aheight that extends between a top surface of the first metal section anda bottom surface of the third metal section, and the height is greaterthan the width.